The present invention relates to an article having a predetermined surface configuration and to a production process therefor. More specifically, it relates to an article having a predetermined surface configuration typified by optical elements such as reflection type diffraction gratings, transmission type diffraction gratings, lens arrays and Fresnel lenses and to a production process therefor.
Optical elements such as diffraction gratings and microlens arrays must have predetermined fine irregularities in the surface.
As means of forming such irregularities in the surface, there is known a method in which an ultraviolet curable resin monomer is uniformly spread over a substrate and exposed to ultraviolet radiation while it is contacted to a mold having irregularities (JP-A 63-49702) (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d).
Also JP-A 62-102445 and JP-A 6-242303 disclose a production process in which irregularities are formed in the surface of a substrate by applying a solution containing silicon alkoxide to a glass substrate, pressing a mold having irregularities against the coating film and heating.
However, in the technology of the above JP-A 63-49702, the ultraviolet curable monomer has large shrinkage in the photopolymerization step and therefore may not achieve high accuracy required for an optical element. The monomer also has a problem with heat resistance.
In contrast to this, an optical element obtained by thermally curing silicon alkoxide has excellent heat resistance but it has large shrinkage in the hydrolysis/polycondensation reaction step and therefore may not achieve high accuracy required for an optical element.
It is an object of the present invention to provide an article having a predetermined surface configuration, such as an optical element having fine irregularities in the surface, which has high heat resistance, small thermal shrinkage at the time of molding a film and high dimensional accuracy, by solving the above problems existent in the prior art.
It is another object of the present invention to provide an industrially advantageous process for producing the above article of the present invention.
Other objects and advantages of the present invention will become apparent from the following description.
According to the present invention, firstly, the above objects and advantages of the present invention are attained by a process for producing an article having a predetermined surface configuration, comprising the steps of:
setting a composition comprising a compound which contains a dimethylsiloxane skeleton having at least three recurring units and at least one polymerizable organic group in the molecule between and in contact with the surface of a substrate and the molding surface of a mold in the form of a film;
applying at least one of heat and ultraviolet radiation to the composition set in the form of a film;
removing the mold and, as required, heating the film; and
forming the article in which the surface of the substrate is covered with a film having a surface configuration which is the inversion of the surface configuration of the mold.
According to the present invention, secondly, the above objects and advantages of the present invention are attained by an article having a predetermined surface configuration, comprising a substrate and an organopolysiloxane film having a predetermined uneven surface and a maximum thickness of 1 xcexcm to 1 mm formed on the surface of the substrate, wherein the organopolysiloxane film contains 10 to 50 wt % of a methyl group, 1 to 30 wt % of a polymerized segment of a polymerizable organic group and 45 to 89 wt % of a Sixe2x80x94O bonding segment, the total of the methyl group and the polymerized segment of the polymerizable organic group being 11 to 55 wt %.
The present invention will be described in detail hereinunder. A description is first given of the production process of the present invention.
The composition used in the process of the present invention comprises a compound having linear and branched dimethylsiloxane skeletons having three or more recurring units. The dimethylsiloxane skeletons contribute to the heat resistance and low shrinkage of the obtained film. When the number of recurring units represented byxe2x80x94((CH3)2Sixe2x80x94O)xe2x80x94 is too small, the viscosity of a liquid composition becomes too low and when the number of the recurring units is too large, the viscosity of the liquid composition becomes too high. In any case, coating and other works and handling become difficult. The number of the recurring units is preferably 3 to 200, more preferably 3 to 100, the most preferably 3 to 50. The compound also has at least one polymerizable organic group in the molecule. Photopolymerization (or thermopolymerization) is caused by the addition polymerization of a radical or cation formed by the optical (or thermal) decomposition of an initiator to the polymerizable organic group. Therefore, shrinkage is smaller than in a dehydration condensation reaction and a chemically bonded uniform organic-inorganic composite film can be formed instantaneously. Consequently, an organic group which is polymerized by light or heat is used as the polymerizable organic group. Examples of the photopolymerizable organic group include acryloxy group, methacryloxy group, vinyl group, epoxy group and organic groups containing these. Examples of the thermopolymerizable organic group include vinyl group, epoxy group and organic groups containing these. At least two of these groups are preferably contained in the molecule of the above compound when the polymerizable organic group is an acryloxy group, methacryloxy group or vinyl group. Organic groups containing an acryloxy group include acryloxy group-substituted alkyl groups such as acryloxypropyl group and acryloxy group-substituted hydroxyalkyl groups. Organic groups containing a methacryloxy group include methacryloxy group-substituted alkyl groups, methacryloxyethoxy group and methacryloxypolyethylene group. Organic groups containing a vinyl group include vinylbenzyloxy group, N-vinylformamide group and vinyloxy group. Organic groups containing an epoxy group include epoxy group-substituted propoxy groups, epoxycyclohexylethyl group and epoxyethylphenyl group. Since heat resistance and humidity resistance lower when too many polymerizable organic groups are contained in the molecule, the number of polymerizable organic groups in the molecule is preferably 50 or less.
The above compound is, for example, a dimethylpolysiloxane having a polymerizable organic group at both terminals represented by the following formula (1): 
wherein R1 and R2 are each independently a vinyl group or a group having an acryloxy group, methacryloxy group or epoxy group, and n is an integer of 3 to 200, or a dimethylpolysiloxane having a trimethylsilyl group at both terminals and two or more polymerizable organic groups represented by the following formula (2): 
wherein R3 is a vinyl group or a group having an acryloxy group, methacryloxy group or epoxy group, m is an integer of 2 to 200, n is an integer of 1 to 50 when R3 is an epoxy group and an integer of 2 to 50 when R3 is another group, with the proviso that m+n is 3 to 200.
Illustrative examples of the compound include (acryloxypropyl)methylsiloxane-dimethylsiloxane copolymer, (methacryloxypropyl)methylsiloxane-dimethylsiloxane copolymer, vinylmethylsiloxane-dimethylsiloxane copolymer and (epoxycyclohexylethyl)methylsiloxane-dimethylsiloxane copolymer.
Out of these compounds, a polydimethylpolysiloxane having a linear acryloxypropyl group at both terminals (the number of recurring units represented by (xe2x80x94((CH3)2Sixe2x80x94O)xe2x80x94 is 3 to 50) and a polydimethylpolysiloxane having a linear methacryloxypropyl group at both terminals (the number of recurring units represented by (xe2x80x94((CH3)2Sixe2x80x94O)xe2x80x94 is 3 to 50) are preferred. Out of these, a polydimethylpolysiloxane having a linear acryloxypropyl group at both terminals (the number of the recurring units of this is 10 to 25) and a polydimethylpolysiloxane having a linear methacryloxypropyl group at both terminals (the number of the recurring units of this is 10 to 25) are more preferred. When adhesion between the film and a quartz substrate must be further improved, an epoxysiloxane is preferred and a branched epoxysiloxane is particularly preferred.
The above liquid composition used in the present invention comprises a photopolymerization initiator when the polymerizable organic group of the compound is photopolymerizable. Examples of the radical photopolymerization initiator include [2-hydroxy-2-methyl-1-phenylpropan-1-one], [1-(4-isopropylphenyl)-2-hydroxy-2-methylpropane-1-one], [4-(2-hydroxyethoxy)phenyl-2-(hydroxy-2-propyl ketone)], [2,2-dimethoxy-1,2-diphenylethane-1-one], [1-hydroxy-cyclohexyl-phenyl-ketone], [2-methyl-1 [4-(methylthio)phenyl]-2-morpholinopropane-1-one], [bis(2,6-dimethoxybenzoyl)-2,4,4-trimethyl-pentylphosphine oxide] and [2-benzyl-2-dimethylamino-1-1-(4-morpholinophenyl)-butanone-1]. Examples of the cationic photopolymerization initiator include phenyl-[m-(2-hydroxytetradecyclo)phenyl]iodonium hexafluoroantimonate and diphenyliodonium tetrakis(pentafluorophenyl)borate. The amount of the photopolymerization initiator is preferably 0.1 to 5 wt % based on the total weight of the liquid composition.
The above liquid composition is set between and in contact with the surface of the substrate and the surface of the mold in the form of a film, at least one of heat and ultraviolet radiation is applied to the composition set in the form of a film, the mold is removed, and the composition is heated as required to form an article having a predetermined surface configuration, such as an optical element in which the surface of the substrate is covered with a film having a surface configuration which is the inversion of the surface configuration of the mold. The following two processes are typically used to form the article.
In the first process (to be referred to as xe2x80x9cmold casting processxe2x80x9d hereinafter), the liquid composition is poured over a mold, degasified and assembled with a substrate, at least one of heat and ultraviolet radiation is applied to the assembly, the mold is removed, and the molded product is heated as required. That is, the mold having predetermined fine irregularities in the molding surface is kept horizontal with the molding surface facing up, and the liquid composition having a viscosity of 1 to 200 cSt is poured over the mold to fill depressions in the mold. In place of pouring, the mold may be immersed in a bath of the liquid composition, or the liquid composition may be applied to the molding surface of the mold with a brush. In this state, the liquid composition is maintained at room temperature to 100xc2x0 C. under a reduced pressure of 2 to 5 Pa for 5 to 10 minutes in such a manner that air should not be contained in the liquid composition on the mold in order to remove bubbles or dissolved oxygen contained in the liquid.
Then, the substrate is contacted to the liquid on the mold in such a manner that a gap should not be formed between the liquid composition and the surface of the substrate in order to set the liquid composition between and in contact with the surface of the substrate and the molding surface of the mold in the form of a film, and the liquid composition is maintained at 20 to 100xc2x0 C. for 1 to 30 minutes while it is exposed to ultraviolet radiation or heated at 140 to 250xc2x0 C. for 10 to 120 minutes in that state to be polymerized and cured. In the case of exposure to ultraviolet radiation, at least one of the substrate and the mold is made from a material which transmits ultraviolet radiation. Subsequently, by stripping off and removing the mold, a film of a cured polydimethylsiloxane having irregularities in the surface which are the inversion of irregularities in the surface of the mold is formed in such a state that it is adhered to the surface of the substrate.
This film is finally heated at 180 to 350xc2x0 C. under normal pressure or a reduced pressure of 2 to 5 Pa for 15 to 250 minutes as required to vaporize the residual initiator and unpolymerized product contained in the polysiloxane film with the result that the film is slightly shrunken in volume in a thickness direction to become a compact film. Thus, an article such as an optical element covered with a film having a surface configuration which is the inversion of the surface configuration of the mold is obtained.
In the second molding process (to be referred to as xe2x80x9csubstrate casting processxe2x80x9d hereinafter), the liquid composition is directly poured over the surface of the substrate and degasified, the mold is pressed against the film on the surface of the substrate, the film is exposed to ultraviolet radiation or heated in this state, the surface configuration of the mold is transferred to the surface of the film, the mold is removed, and the film is finally heated as required. That is, the surface to be covered of the substrate is maintained horizontal and the liquid composition having a viscosity of 1 to 200 cSt is poured over the substrate and spread over the surface of the substrate in the form of a film to a predetermined thickness. In this state, the liquid composition is maintained at room temperature to 100xc2x0 C. under a reduced pressure of 2 to 5 Pa for 5 to 10 minutes in such a manner that air should not be contained in the liquid composition filled on the substrate in order to remove bubbles and dissolved oxygen contained in the liquid. Then, the mold having predetermined fine irregularities in the surface is pressed against the liquid composition in the form of a film and kept at a pressure of 0.5 to 120 kg/cm2 and a temperature of 160 to 350xc2x0 C. for 60 seconds to 60 minutes or pressed against the liquid composition at the above pressure and kept at 20 to 100xc2x0 C. for 60 seconds to 30 minutes while it is exposed to ultraviolet radiation at an irradiation intensity of 1.0 to 50 mW/cm2 at an exposed site in this state to almost complete the polymerization reaction of the liquid composition in order to cure it. In the case of exposure to ultraviolet radiation, at least one of the substrate and the mold is made from a material which transmits ultraviolet radiation. Then, by stripping off and removing the mold, a polydimethylsiloxane film which is a cured film having irregularities in the surface which are the inversion of the irregularities of the mold is formed in such a state that it is adhered to the surface of the substrate. Then, the film is heated at 180 to 250xc2x0 C. under normal pressure or a reduced pressure of 2 to 5 Pa for 15 to 350 minutes as required to vaporize the residual photopolymerization initiator and unpolymerized product contained in the polysiloxane film with the result that the film is slightly shrunken in volume in a thickness direction to become a compact film. An article such as an optical element covered with a film having a surface configuration which is the inversion of the surface configuration of the mold is obtained.
A release film made from gold (Au) is preferably formed on the molding surface of the mold used in the present invention. Since gold has excellent releasability for a sol-gel material, mechanical strength high enough to withstand pressure applied to the sol-gel material, heat resistance, corrosion resistance and oxidation resistance, it is excellent as a release film. When the thickness of the gold release film is too small, the number of times of re-use becomes small and when the thickness of the film is too large, mold transferability deteriorates. Therefore, the thickness of the release film is preferably 200 to 1,000 nm, more preferably 400 to 600 nm. Since the release film has higher releasability as its surface becomes smoother, it is preferably formed uniform and smooth by sputtering, vacuum deposition, electroless plating, electrolytic plating or hot foil stamping.
It is preferred to form an adhesion enhancing layer made from at least one metal selected from the group consisting of platinum (Pt), copper (Cu), palladium (Pd) and silver (Ag) under the gold (Au) release film, that is, between the surface of the mold substrate and the above release film. Specifically, a platinum (Pt), copper (Cu), palladium (Pd) or silver (Ag) layer or an alloy layer thereof is formed on the molding surface of the mold substrate to a predetermined thickness before a release film is formed on the surface. The adhesion enhancing layer adheres firmly the release film to the molding surface of the mold and serves as a protective layer for the formation of a pure release film by preventing the molding surface layer (for example, silicon) of the mold substrate from being mixed with the release film at the time of forming the release film. A metal which is excellent in adhesion to the molding surface of the mold substrate and the protection of the surface is platinum (Pt). When the thickness of the adhesion enhancing layer is too small, adhesion between the release film and the molding surface of the mold substrate cannot be increased and the release film is not made from pure gold. When the thickness is too large, the predetermined configuration of the molding surface of the mold substrate changes disadvantageously. Therefore, the adhesion enhancing layer has a thickness of preferably 50 to 400 nm, more preferably 100 to 200 nm. The adhesion enhancing layer is preferably formed uniform and smooth by sputtering, vacuum deposition, electroless plating or electrolytic plating.
At least the molding surface of the above mold substrate is made from at least one material selected from the group consisting of titanium (Ti), aluminum (Al), silicon (Si) and oxides thereof. The mold substrate may be made from titanium, aluminum, silicon, titanium oxide, aluminum oxide or silicon oxide, or may have a prime coat made from at least one material selected from the group consisting of titanium (Ti), aluminum (Al), silicon (Si) and oxides thereof on the surface (surface to be covered with a release film) of a core material of silicon, glass (including quartz glass), resin, metal or composite thereof. When the molding surface of the mold substrate is made from the above material, the release film and the adhesion enhancing layer firmly adhere to the mold substrate, whereby there is no possibility that the release film will peel off from the mold and durability improves. The prime coat has a thickness of preferably 20 to 300 nm, more preferably 50 to 100 nm. The prime coat is preferably formed uniform and smooth by sputtering, vacuum deposition, electroless plating or electrolytic plating. An example of the mold substrate is what is obtained by vacuum depositing titanium on a core member made from silicon or quartz glass.
A material having an expansion coefficient close to that of the release film is preferably selected as the material of the above core member. The core member made from a resin has advantages that it can be finely processed easily and can be easily molded into a desired form. A glass or metal core member has high heat resistance and mechanical strength and excellent durability.
The mold in the present invention has projections or depressions in its molding surface. The projections and depressions are, for example, spherical, conical, pyramid-like or slit-like having a desired section. Any number of spherical, conical or pyramid-like projections may be formed in the entire surface or part of the release film. When slits are formed as depressions, any number of linear or curved slits may be formed. When a plurality of slits are formed, they may be formed concentrically or in a lattice form.
The substrate in the present invention is shaped like a flat board or curved board. It is desired that the surface of the substrate have a warp (the length of thermal deformation in a direction perpendicular to the surface per the unit length in the surface direction of the substrate) at 200xc2x0 C. and 20xc2x0 C. of xc2x15 xcexcm or less per 1 cm. When the warp is above this range, the film may peel off from the substrate or the film may crack in the film molding step. Therefore, it is preferred to select the material, size and shape of the substrate.
Preferably, this substrate has a linear expansion coefficient of 1.5xc3x9710xe2x88x925/xc2x0 C. or less. When the linear expansion coefficient of the substrate is larger than 1.5xc3x9710xe2x88x925/xc2x0 C., in the case of a plastic substrate having a high thermal expansion coefficient, such as polypropylene (9 to 15xc3x9710xe2x88x925/xc2x0 C.), the film may peel off from the surface of the substrate or the film may crack in the step of molding an organopolysiloxane film. General inorganic glass has a linear expansion coefficient of 1.5xc3x9710xe2x88x925/xc2x0 C. or less. At least the surface of the substrate is preferably made from an oxide. If the surface in contact with the organopolysiloxane film of the substrate is not made from an oxide, the adhesion strength of the substrate will lower in the step of molding a film, whereby the film will readily peel off from the substrate. Preferred examples of the material of the substrate include oxide glasses such as silicate-based glass exemplified by float glass, borate-based glass and phosphate-based glass, quartz, ceramics, silicon, metals such as aluminum, epoxy resin and glass fiber reinforced polystyrene. Although the organopolysiloxane film does not adhere to a metal as it is, when the surface of a metal is treated with an oxidizing agent, it can be used as the substrate.
When a transparent object which transmits light having a desired wavelength, such as visible range, ultraviolet range or infrared range is used as the substrate in the present invention, the article obtained by the present invention can function as a transmission type optical element such as a lens array, diffraction grating (such as an echelette diffraction grating, echelon diffraction grating or echelle diffraction grating) or Fresnel lens. When a transparent or non-transparent object is used as the substrate, a reflection type optical element such as a diffraction grating, diffuser or Fresnel mirror, or other information recording medium such as CD-ROM can be obtained by forming a metal (such as aluminum or silver) or dielectric film (such as magnesium fluoride or titanium oxide) on the organopolysiloxane film.
When an inorganic substrate made from oxide glass such as silicate-based glass, borate-based glass or phosphate-based glass, quartz, ceramic, silicon or metal such as aluminum is used as the substrate in the present invention, it is desired that a film, preferably a 5 to 200 nm-thick film containing a silane coupling agent be formed by applying a surface treating composition containing a silane coupling agent to the surface of the substrate before use.
The silane coupling agent is, for example, a silicon compound having an organic functional group represented by the following formula (3):
R4R5kSi(R6)3xe2x88x92kxe2x80x83xe2x80x83(3)
wherein R4 is an organic group having a methacryl group, acryl group, epoxy group, allyl group, mercapto group or amino group, or a vinyl group, R5 is an alkyl group such as methyl group or ethyl group, R6 is a group or atom having hydrolyzability, and k is 0 or 1. Examples of the above organic group having a methacryl group, acryl group, epoxy group, ally group, mercapto group or amino group include organic groups obtained by substituting the hydrogen of an alkyl group (such as alkyl group having 1 to 3 carbon atoms) by these groups. R6 (group or atom having hydrolyzability) is an alkoxyl group, alkoxyalkoxyl group, acetoxyl group, amide group, oxime group, propenoxyl group or chlorine atom.
Illustrative examples of the silicon compound represented by the above formula (3) as the silane coupling agent are given below. They include acryl functional silanes, epoxy functional silanes, methacryl functional silanes, allyl functional silanes, mercapto functional silanes, amino functional silanes and vinyl functional silanes. The acryl functional silanes (R4 in the above formula (3) is an organic group having an acryl group) include 3-acryloxypropyl trimethoxysilane, 3-acryloxypropylmethyl dimethoxysilane, 3-acryloxypropyl triethoxysilane and 3-acryloxypropylmethyl diethoxysilane. The epoxy functional silanes (R4 in the above formula (3) is an organic group having an epoxy group) include 3-glycidoxypropyl trimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyl trimethoxysilane and 2-(3,4-epoxycyclohexyl)ethyl triethoxysilane. The methacryl functional silanes (R4 in the above formula (3) is an organic group having a methacryl group) include 3-methacryloxypropyl trimethoxysilane, 3-methacryloxypropyl triethoxysilane, 3-methacryloxypropylmethyl dimethoxysilane, 3-methacryloxypropylmethyl diethoxysilane, 3-methacryloxyundecyl trimethoxysilane and 3-methacryloxyethyloxypropyl trimethoxysilane. The allyl functional silanes (R4 in the above formula (3) is an organic group having an ally group) include allyl triethoxysilane, allyl trichlorosilane, allyl trimethoxysilane and allylphenyl dichlorosilane. The mercapto functional silanes (R4 in the above formula (3) is an organic group having a mercapto group) include 3-mercaptopropyl trimethoxysilane. The amino functional silanes (R4 in the above formula (3) is an organic group having an amino group) include 3-aminopropyl trimethoxysilane. The vinyl functional silanes (R4 in the above formula (3) is a vinyl group) include vinyl trimethoxysilane, vinyl triethoxysilane, vinyl tris (xcex2-methoxyethoxy)silane, vinyl triacetoxysilane and vinyl trichlorosilane.
The surface treating composition may contain a compound represented by the following formula (4):
M(R7)pxe2x80x83xe2x80x83(4)
wherein M is silicon, titanium, zirconium or aluminum, R7 is a group or atom having hydrolyzability, and p is 4 when M is silicon, titanium or zirconium and 3 when M is aluminum, or a hydrolyzate thereof, besides the silane coupling agent.
Examples of R7 (group or atom having hydrolyzability) include alkoxyl group, alkoxyalkoxyl group, acyloxy group, acetoxyl group and chlorine atom. By containing this compound, the film containing a silane coupling agent formed on the surface of the substrate is more firmly adhered to the surface of the substrate. When the content of the compound is too low, the effect of increasing this adhesion is small and when the content is too high, the effect of the silane coupling agent itself lowers. Therefore, the compound represented by the formula (4) (or its hydrolyzate) is preferably contained in the surface treating composition in an amount of 5 to 50 parts by weight based on 100 parts by weight of the silane coupling agent.
Out of the compounds represented by the above formula (4), compounds in which M is silicon include tetraethoxysilane, tetramethoxysilane, tetra-2-methoxyethoxysilane, tetraacetoxysilane and tetrachlorosilane.
Out of the compounds represented by the above formula (4), compounds in which M is titanium include tetramethoxy titanium, tetraethoxy titanium, tetraisopropoxy titanium, tetraisopropoxy titanium isopropanol complex, tetra-n-propoxy titanium, tetraisobutoxy titanium, tetra-n-butoxy titanium, tetra-sec-butoxy titanium, tetra-t-butoxy titanium, tetra(2-ethylhexyloxy)titanium and tetrastearyloxy titanium.
Out of the compounds represented by the above formula (4), compounds in which M is zirconium include tetramethoxy zirconium, tetraethoxy zirconium, tetraisopropoxy zirconium, tetra-n-propoxy zirconium, tetraisopropoxy zirconium-isopropanol complex, tetraisobutoxy zirconium, tetra-n-butoxy zirconium, tetra-sec-butoxy zirconium and tetra-t-butoxy zirconium.
Out of the compounds represented by the above formula (4), compounds in which M is aluminum include trimethoxy aluminum, triethoxy aluminum, triisopropoxy aluminum, tri-n-propoxy aluminum, triisobutoxy aluminum, tri-n-butoxy aluminum, tri-sec-butoxy aluminum and tri-t-butoxy aluminum.
The hydrolyzate of the compound represented by the above formula (4) include hydrolyzates obtained by substituting some or all of R7""s in the above compound by a hydroxyl group and hydrolyzates obtained by the natural condensation of some of the substituted hydroxyl groups. These hydrolyzates can be easily obtained by hydrolyzing the compound in a mixed solvent of water and an alcohol in the presence of an acid.
The surface treating composition comprises an alcohol as an essential component and further an acid catalyst and water as optional components, in addition to the above silane coupling agent and optionally the compound represented by the above formula (4) (or a hydrolyzate thereof) to be contained.
The above acid catalyst is not always necessary when the above silane coupling agent and the compound represented by the above formula (4) are already hydrolyzed. However, when they are not hydrolyzed, the acid catalyst is preferably contained as a catalyst for the hydrolysis and dehydration of the above components. Although the type of the acid catalyst is not particularly limited, an acid catalyst which is easily vaporized by drying and hardly remains in the film is preferred because the film can be made hard. Examples of the acid catalyst include hydrochloric acid, nitric acid, acetic acid, hydrofluoric acid, formic acid and trifluoroacetic acid. The amount of the acid is preferably 10xe2x88x925 to 10 parts by weight, more preferably 10xe2x88x923 to 1 part by weight based on 100 parts by weight of the silane coupling agent.
The above water is not always necessary when the above silane coupling agent and the compound represented by the above formula (4) are already hydrolyzed. However, when they are not hydrolyzed, water is preferably contained in the surface treating composition for the hydrolysis of these components. The amount of water is 10 to 300 parts by weight based on 100 parts by weight of the silane coupling agent, including a water solvent for the compound represented by the above formula (4) and water contained in the alcohol to be described hereinafter as an impurity.
Although the above alcohol solvent is not particularly limited, it is, for example, methanol, ethanol, 1-propanol, 2-propanol, butyl alcohol or amyl alcohol. Out of these, chain saturated monohydric alcohols having 3 or less carbon atoms such as methanol, ethanol, 1-propanol and 2-propanol are preferred because their vaporization rates at normal temperature are high. The amount of the alcohol, which differs according to coating technique and desired film thickness, is preferably 500 to 10,000 parts by weight based on 100 parts by weight of the silane coupling agent.
The technique for applying the surface treating composition is not particularly limited. Dip coating, flow coating, curtain coating, spin coating, spray coating, bar coating, roll coating or brush coating may be used.
The surface treating composition is applied at a temperature of 0 to 40xc2x0 C., for example, room temperature and a relative humidity of 40% or less. After application, the coating film is dried at a temperature of 0 to 40xc2x0 C., for example, room temperature and a relative humidity of 40% or less for 10 seconds to 20 minutes. Subsequently, it may be heated at a temperature higher than room temperature to 30xc2x0 C. for 30 seconds to 10 minutes as required.
The preferred composition of the surface treating composition based on the silicon compound represented by the above formula (3) is as follows.
Silicon compound represented by the formula (3): 100 parts by weight
Compound represented by the above formula (4): 5 to 50 parts by weight
Water: 10 to 300 parts by weight
Acid catalyst: 10xe2x88x925 to 10 parts by weight
Solvent (alcohol): 500 to 10,000 parts by weight
According to the present invention, an organopolysiloxane film having heat resistance high enough to stand a temperature of 350xc2x0 C., a maximum thickness (thickness measured at a depression portion in the surface) of 1 xcexcm to 1 mm, preferably 20 to 150 xcexcm, a refractive index of 1.50 to 1.54 which is close to the refractive index of ordinary glass and fine surface irregularities, for example, those having a predetermined height of 5 to 500 xcexcm and a predetermined width (pitch of irregularities) of 1 to 500 xcexcm is formed on the substrate which is shaped like a flat board or curved board and whose surface has been treated with a silane coupling agent.
The dimethylpolysiloxane film which comprises this film contains 10 to 50 wt % of a methyl group, 1 to 30 wt % of a polymerized segment of a polymerizable organic group and 45 to 89 wt % of a Sixe2x80x94O structural segment. The total of the methyl group and the polymerized segment of the polymerizable organic group is 11 to 55 wt %.
This film is elastic (little brittle), has high strength and hardly cracks. Since bubbles formed by molding are not seen in the film and the shrinkage of the film at the time of molding is small, excellent transferability with extremely high dimensional accuracy of fine irregularities in the surface of the film can be achieved. Stated more specifically, when a large number of projections having a height of 20 to 100 xcexcm, for example, are formed, height variations among the projections in the surface of the film are 1 xcexcm or less. The deviation of the interval between projections in the surface of the film from that of the mold is measurement accuracy (0.2 xcexcm) or less.
When the optical element of the present invention is used as a reflection type optical element, a reflection increasing film is preferably formed on the surface of the optical element. The reflection increasing film is a thin film of metal such as gold, silver, platinum or aluminum or a laminate formed by alternately piling up dielectric thin films having a high refractive index and a low refractive index. The dielectric thin film having a high refractive index is made from tantalum oxide, titanium oxide, zirconium oxide or hafnium oxide. Out of these, tantalum oxide stable to laser beams is preferably used. The dielectric thin film having a low refractive index is made from silica or magnesium fluoride. A combination of a metal thin film and a dielectric multi-layer film may be used. The refractive index and thickness of the thin film are adjusted such that the operation wavelength of the reflection type optical element and the wavelength of the reflection peak of the reflection increasing film agree with each other. When the optical element is used as a transmission type optical element, an anti-reflection film is preferably formed at the interface with air. The anti-reflection film is a laminate formed by alternately piling up dielectric thin films having a high refractive index and a low refractive index or an anti-reflection structure having a fine cyclic structure of 1 xcexcm or less.
The coating film of the article having a predetermined surface configuration such as an optical element obtained by the present invention is made from a matrix containing silicon and oxygen, some of the above silicon atoms are bonded to other silicon atoms through a first polyhydrocarbon group having at least 4 carbon atoms (such as a group obtained by polymerizing two acryloxypropyl groups), and some of the above silicon atoms are directly bonded to a second monohydrocarbon group (methyl group). Since an organic segment and an inorganic segment are thus bonded together, a material for an optical element having excellent heat resistance and moldability is provided. By changing the contents of the first polyhydrocarbon group and the second monohydrocarbon group, the refractive index of the transmission type optical element can be adjusted. When the total content of the first polyhydrocarbon group and the second monohydrocarbon group is too high, they exert an influence upon heat resistance. Therefore, the total content is preferably 55 wt % or less.
The first polyhydrocarbon group combines the first silicon atom with the second silicon atom and may contain a hetero atom such as oxygen atom, nitrogen atom or sulfur atom in addition to carbon atom and hydrogen atom. The oxygen atom and nitrogen atom serve to increase the bonding force of the matrix and improve bonding force between the matrix and the surface of the substrate through chemical bonding such as ion bonding or hydrogen bonding. The second monohydrocarbon group may contain a hetero atom such as oxygen atom, nitrogen atom or sulfur atom in addition to carbon atom and hydrogen atom. It may also contain fluorine atom or another halogen atom. By using fluorine atom, the refractive index can be reduced and hydrophobic nature can be provided, thereby making it possible to improve the water resistance of the optical element.